Thread: Jinxed?

Originally Posted by BobD

Here is my understanding of roughly how the VDC works.


There is a pressure control valve (PCV) which diverts compressor pressure to operate the variable displacement swash plate. If there is not enough pressure when the displacement is at minimum when it starts the swashplate won't tilt to increase the displacement, hence cooling won't start. Once it starts to tilt the pressure rapidly increases and then the wear in the valve doesn't matter.


I think it takes lowered pressure due to compressor wear plus a worn PCV to cause the issues to start. Sometimes replacing the PCV will fix it for a short time but the valve is usually stuffed from general wear of everything else so a new one doesn't last long, from what I read. Hence I asked for a new compressor which has fixed the problem 100% over the last 20,000km of high temperature driving.


It is enlightening to look up variable displacement compressors and see how they work. I assume that the LR version is externally controlled by an ECU and not internally controlled as older types were.

Hey Rich,
I had the "Black death" issue in the A/C unit about 4 or 5 years ago and at the time the repairer, a gentleman in his 60's whom had been repairing Ac's most of his working life, commented that alot of the new Ac's had the "high efficiency" condensors and he was off the belief that leaving the Ac running when you shut the vehicle down so that it was engaged at start up was one of the major causes of the "black death". It was years ago now so i'm a little sketchy on detail but it went something on the line of what BobD has posted here, it's about incorrect pressures at start up for a few seconds combined with the very small bore diameter of the high efficiency condensors being easily blocked. Since that conversation I have always turned the Ac off before I shut down the vehicle and don't turn it until after the vehicle was running. Obviously I can't prove that this is extending the life of the Ac but 140 000k's later through some pretty demanding environments and the Ac is still going strong.

Maybe good info, maybe old wives tail but it's part of the shut down procedure now LOL.
I hope you don't have anymore problems with it, at that price, you wouldn't want it to be a regular recurring event ..
good luck
regards
Brian

Mine didn't start reducing its efficiency until about 190,000 km. Even then it still worked, just a delayed start and slightly reduced cooling. At least it didn't fail catastrophically as per Rich's compressor.